Thermochromic VO2 films deposited by RF magnetron sputtering using V2O3 orV2O5 targets

Thermochromic monoclinic-tetragonal VO2 films were successfully deposited o n glass substrates with high reproducibility by rf magnetron sputtering usi ng V2O3 or V2O5 targets. In the case of reactive sputtering using a V-metal target, the VO2 films could be obtained only under the very narrow deposit ion conditions of the "transition region" where the deposition rate decreas es drastically with increasing oxygen gas flow rate. In the case of a V2O3 target, polycrystalline VO2 films with a thickness of 400 to 500 nm were ob tained by the introduction of oxygen gas [O-2/(Ar + O-2) = 1-1.5%], whereas hydrogen gas [H-2/(Ar + H-2) = 2.5-10%] was introduced in the case of a V2 O5 target. Furthermore, the VO2 films were successfully grown heteroepitaxi ally on a single-crystal sapphire [alpha -Al2O3(001)] substrate, where the epitaxial relationship was confirmed to be VO2(010)[100] parallel to Al2O3( 001)[100], [010], [(1) over bar(1) over bar0] by an X-ray diffraction pole figure measurement. The resistivity ratio between semiconductor and metal p hases for the heteroepitaxial VO2 films was much larger than the ratio of t he polycrystalline films on glass substrates under the same deposition cond itions.